First Steps in JDBC

This section describes how to get up and running with the Oracle JDBC drivers. When using the Oracle JDBC drivers, you must include certain driver-specific information in your programs. This section describes, in the form of a tutorial, where and how to add the information. The tutorial guides you through creating code to connect to and query a database from the client.

To connect to and query a database from the client, you must provide code for these tasks:

1. Import Packages

2. Register the JDBC Drivers

3. Open a Connection to a Database

4. Create a Statement Object

5. Execute a Query and Return a Result Set Object

6. Process the Result Set

7. Close the Result Set and Statement Objects

8. Make Changes to the Database

9. Commit Changes

10. Close the Connection

You must supply Oracle driver-specific information for the first three tasks, which allow your program to use the JDBC API to access a database. For the other tasks, you can use standard JDBC Java code as you would for any Java application.

Import Packages

Regardless of which Oracle JDBC driver you use, include the following import statements at the beginning of your program (java.math only if needed):

import java.sql.*;	for standard JDBC packages
import java.math.*;	for BigDecimal and BigInteger classes

Import the following Oracle packages when you want to access the extended functionality provided by the Oracle drivers. However, they are not required for the example presented in this section:

import oracle.jdbc.driver.*; import oracle.sql.*;

for Oracle extensions to JDBC

For an overview of the Oracle extensions to the JDBC standard, see Chapter 6, "Overview of Oracle Extensions".

Register the JDBC Drivers

You must provide the code to register your installed driver with your program. You do this with the static registerDriver() method of the JDBC DriverManager class. This class provides a basic service for managing a set of JDBC drivers.

Note: Alternatively, you can use the forName() method of the java.lang.Class class to load the JDBC drivers directly. For example: Class.forName ("oracle.jdbc.driver.OracleDriver"); However, this method is valid only for JDK-compliant Java virtual machines. It is not valid for Microsoft Java virtual machines.

Because you are using one of Oracle's JDBC drivers, you declare a specific driver name string to registerDriver(). You register the driver only once in your Java application.

DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver());

Open a Connection to a Database

Open a connection to the database with the static getConnection() method of the JDBC DriverManager class. This method returns an object of the JDBC Connection class that needs as input a user name, password, connect string that identifies the JDBC driver to use, and the name of the database to which you want to connect.

Connecting to a database is a step where you must enter Oracle JDBC driver-specific information in the getConnection() method. If you are not familiar with this method, continue reading the "Understanding the Forms of getConnection()" section below.

If you are already familiar with the getConnection() method, you can skip ahead to either of these sections, depending on the driver you installed:

• "Opening a Connection for the JDBC OCI Driver"

• "Opening a Connection for the JDBC Thin Driver"

  Notes: With JDK 1.2, using JNDI (Java Naming and Directory Interface) is becoming the recommended way to make connections. See "A Brief Overview of Oracle Data Source Support for JNDI" and "Creating a Data Source Instance, Registering with JNDI, and Connecting". If you are using the Thin driver, be aware that it does not support OS authentication in making the connection. As a result, special logins are not supported. This discussion in this section does not apply to the server-side internal driver, which uses an implicit connection. See "Connecting to the Database with the Server-Side Internal Driver".

Understanding the Forms of getConnection()

The DriverManager class getConnection() method whose signatures and functionality are described in the following sections:

• "Specifying a Database URL, User Name, and Password"

• "Specifying a Database URL That Includes User Name and Password"

• "Specifying a Database URL and Properties Object"

If you want to specify a database name in the connection, it must be in one of the following formats:

• a Net8 keyword-value pair

• a string of the form <host_name>:<port_number>:<sid> (Thin driver only)

• a TNSNAMES entry (OCI driver only)

For information on how to specify a keyword-value pair or a TNSNAMES entry, see your Net8 Administrator's Guide.

Specifying a Database URL, User Name, and Password

The following signature takes the URL, user name, and password as separate parameters:

getConnection(String URL, String user, String password);

Where the URL is of the form:

jdbc:oracle:<drivertype>:@<database>

The following example connects user scott with password tiger to a database with SID orcl through port 1521 of host myhost, using the Thin driver.

Connection conn = DriverManager.getConnection
                  ("jdbc:oracle:thin:@myhost:1521:orcl", "scott", "tiger");

If you want to use the default connection for an OCI driver, specify either:

Connection conn = DriverManager.getConnection 
                  ("jdbc:oracle:oci8:scott/tiger@");

or:

Connection conn = DriverManager.getConnection 
                  ("jdbc:oracle:oci8:@", "scott", "tiger");

For all JDBC drivers, you can also specify the database with a Net8 keyword-value pair. The Net8 keyword-value pair substitutes for the TNSNAMES entry. The following example uses the same parameters as the preceding example, but in the keyword-value format:

Connection conn = DriverManager.getConnection
                  (jdbc:oracle:oci8:@MyHostString","scott","tiger");

or:

Connection conn = DriverManager.getConnection
   ("jdbc:oracle:oci8:@(description=(address=(host= myhost)
   (protocol=tcp)(port=1521))(connect_data=(sid=orcl)))","scott", "tiger");

Specifying a Database URL That Includes User Name and Password

The following signature takes the URL, user name, and password all as part of a URL parameter:

getConnection(String URL);

Where the URL is of the form:

jdbc:oracle:<drivertype>:<user>/<password>@<database>

The following example connects user scott with password tiger to a database on host myhost using the OCI driver. In this case, however, the URL includes the userid and password, and is the only input parameter.

Connection conn = DriverManager.getConnection
                        ("jdbc:oracle:oci8:scott/tiger@myhost);

If you want to connect with the Thin driver, you must specify the port number and SID. For example, if you want to connect to the database on host myhost that has a TCP/IP listener up on port 1521, and the SID (system identifier) is orcl:

Connection conn = DriverManager.getConnection
                        ("jdbc:oracle:thin:scott/tiger@myhost:1521:orcl);

Specifying a Database URL and Properties Object

The following signature takes a URL, together with a properties object that specifies user name and password (perhaps among other things):

getConnection(String URL, Properties info);

Where the URL is of the form:

jdbc:oracle:<drivertype>:@<database>

In addition to the URL, use an object of the standard Java Properties class as input. For example:

java.util.Properties info = new java.util.Properties();
info.put ("user", "scott");
info.put ("password","tiger");
info.put ("defaultRowPrefetch","15");
getConnection ("jdbc:oracle:oci8:@",info);

Table 3-1 lists the connection properties that Oracle JDBC drivers support.

Table 3-1 Connection Properties Recognized by Oracle JDBC Drivers

Name	Short Name	Type	Description
user	n/a	String	the user name for logging into the database
password	n/a	String	the password for logging into the database
database	server	String	the connect string for the database
internal_logon	n/a	String	a role, such as sysdba or sysoper, that allows you to log on as sys
defaultRowPrefetch	prefetch	String (containing integer value)	the default number of rows to prefetch from the server (default value is "10")
remarksReporting	remarks	String (containing boolean value)	"true" if getTables() and getColumns() should report TABLE_REMARKS; equivalent to using setRemarksReporting() (default value is "false")
defaultBatchValue	batchvalue	String (containing integer value)	the default batch value that triggers an execution request (default value is "10")
includeSynonyms	synonyms	String (containing boolean value)	"true" to include column information from predefined "synonym" SQL entities when you execute a DataBaseMetaData getColumns() call; equivalent to connection setIncludeSynonyms() call (default value is "false")

See Table 18-4, "OCI Driver Client Parameters for Encryption and Integrity" and Table 18-5, "Thin Driver Client Parameters for Encryption and Integrity" for descriptions of encryption and integrity drivers.

Using Roles for Sys Logon

To specify the role (mode) for sys logon, use the internal_logon connection property. (See Table 3-1, "Connection Properties Recognized by Oracle JDBC Drivers", for a complete description of this connection property.) To logon as sys, set the internal_logon connection property to sysdba or sysoper.

Note: The ability to specify a role is supported only for sys user name.

Example

The following example illustrates how to use the internal_logon and sysdba arguments to specify sys logon.

//import packages and register the driver
import java.sql.*;
import java.math.*;
DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver());

//specify the properties object
java.util.Properties info = new java.util.Properties();
info.put ("user", "sys");
info.put ("password", "change_on_install");
info.put ("internal_logon","sysdba");

//specify the connection object 
Connection conn = DriverManager.getConnection
                        ("jdbc:oracle:thin:@database",info);
...

Properties for Oracle Performance Extensions

Some of these properties are for use with Oracle performance extensions. Setting these properties is equivalent to using corresponding methods on the OracleConnection object, as follows:

• Setting the defaultRowPrefetch property is equivalent to calling setDefaultRowPrefetch().

  See "Oracle Row Prefetching".

• Setting the remarksReporting property is equivalent to calling setRemarksReporting().

  See "DatabaseMetaData TABLE_REMARKS Reporting".

• Setting the defaultBatchValue property is equivalent to calling setDefaultExecuteBatch().

  See "Oracle Update Batching".

Example

The following example shows how to use the put() method of the java.util.Properties class, in this case to set Oracle performance extension parameters.

//import packages and register the driver
import java.sql.*;
import java.math.*;
DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver());

//specify the properties object
java.util.Properties info = new java.util.Properties();
info.put ("user", "scott");
info.put ("password", "tiger");
info.put ("defaultRowProfetch","20");
info.put ("defaultBatchValue", "5");

//specify the connection object 
Connection conn = DriverManager.getConnection
                        ("jdbc:oracle:thin:@database",info);
...

Opening a Connection for the JDBC OCI Driver

For the JDBC OCI driver, you can specify the database by a TNSNAMES entry. You can find the available TNSNAMES entries listed in the file tnsnames.ora on the client computer from which you are connecting. On Windows NT, this file is located in the [ORACLE_HOME]\NETWORK\ADMIN directory. On UNIX systems, you can find it in the /var/opt/oracle directory.

For example, if you want to connect to the database on host myhost as user scott with password tiger that has a TNSNAMES entry of MyHostString, enter:

Connection conn = DriverManager.getConnection 
                  ("jdbc:oracle:oci8:@MyHostString", "scott", "tiger");

Note that both the ":" and "@" characters are necessary.

For the JDBC OCI and Thin drivers, you can also specify the database with a Net8 keyword-value pair. This is less readable than a TNSNAMES entry but does not depend on the accuracy of the TNSNAMES.ORA file. The Net8 keyword-value pair also works with other JDBC drivers.

For example, if you want to connect to the database on host myhost that has a TCP/IP listener up on port 1521, and the SID (system identifier) is orcl, use a statement such as:

Connection conn = DriverManager.getConnection
   ("jdbc:oracle:oci8:@(description=(address=(host= myhost)
   (protocol=tcp)(port=1521))(connect_data=(sid=orcl)))","scott", "tiger");

Note: Oracle JDBC does not support login timeouts. Calling the static DriverManager.setLoginTimeout() method will have no effect.

Opening a Connection for the JDBC Thin Driver

Because you can use the JDBC Thin driver in applets that do not depend on an Oracle client installation, you cannot use a TNSNAMES entry to identify the database to which you want to connect. You have to either:

• Explicitly list the host name, TCP/IP port and Oracle SID of the database to which you want to connect.

or:

• Use a keyword-value pair list.

  Note: The JDBC Thin driver supports only the TCP/IP protocol.

For example, use this string if you want to connect to the database on host myhost that has a TCP/IP listener on port 1521 for the database SID (system identifier) orcl. You can logon as user scott, with password tiger:

Connection conn = DriverManager.getConnection 
                  ("jdbc:oracle:thin:@myhost:1521:orcl", "scott", "tiger"); 

You can also specify the database with a Net8 keyword-value pair. This is less readable than the first version, but also works with the other JDBC drivers.

Connection conn = DriverManager.getConnection 
    ("jdbc:oracle:thin:@(description=(address=(host=myhost)
    (protocol=tcp)(port=1521))(connect_data=(sid=orcl)))", "scott", "tiger"); 

Notes: Oracle JDBC does not support login timeouts. Calling the static DriverManager.setLoginTimeout() method will have no effect.

Create a Statement Object

Once you connect to the database and, in the process, create your Connection object, the next step is to create a Statement object. The createStatement() method of your JDBC Connection object returns an object of the JDBC Statement class. To continue the example from the previous section where the Connection object conn was created, here is an example of how to create the Statement object:

Statement stmt = conn.createStatement();

Note that there is nothing Oracle-specific about this statement; it follows standard JDBC syntax.

Execute a Query and Return a Result Set Object

To query the database, use the executeQuery() method of your Statement object. This method takes a SQL statement as input and returns a JDBC ResultSet object.

To continue the example, once you create the Statement object stmt, the next step is to execute a query that populates a ResultSet object with the contents of the ENAME (employee name) column of a table of employees named EMP:

ResultSet rset = stmt.executeQuery ("SELECT ename FROM emp");

Again, there is nothing Oracle-specific about this statement; it follows standard JDBC syntax.

Process the Result Set

Once you execute your query, use the next() method of your ResultSet object to iterate through the results. This method steps through the result set row by row, detecting the end of the result set when it is reached.

To pull data out of the result set as you iterate through it, use the appropriate getXXX() methods of the ResultSet object, where XXX corresponds to a Java datatype.

For example, the following code will iterate through the ResultSet object rset from the previous section and will retrieve and print each employee name:

while (rset.next())
   System.out.println (rset.getString(1));

Once again, this is standard JDBC syntax. The next() method returns false when it reaches the end of the result set. The employee names are materialized as Java strings.

For a complete sample application showing how to execute a query and print the results, see "Listing Names from the EMP Table--Employee.java".

Close the Result Set and Statement Objects

You must explicitly close the ResultSet and Statement objects after you finish using them. This applies to all ResultSet and Statement objects you create when using the Oracle JDBC drivers. The drivers do not have finalizer methods; cleanup routines are performed by the close() method of the ResultSet and Statement classes. If you do not explicitly close your ResultSet and Statement objects, serious memory leaks could occur. You could also run out of cursors in the database. Closing a result set or statement releases the corresponding cursor in the database.

For example, if your ResultSet object is rset and your Statement object is stmt, close the result set and statement with these lines:

rset.close();
stmt.close();

When you close a Statement object that a given Connection object creates, the connection itself remains open.

Note: Typically, you should put close() statements in a finally clause.

Make Changes to the Database

To write changes to the database, such as for INSERT or UPDATE operations, you will typically create a PreparedStatement object. This allows you to execute a statement with varying sets of input parameters. The prepareStatement() method of your JDBC Connection object allows you to define a statement that takes variable bind parameters, and returns a JDBC PreparedStatement object with your statement definition.

Use setXXX() methods on the PreparedStatement object to bind data into the prepared statement to be sent to the database. The various setXXX() methods are described in "Standard setObject() and Oracle setOracleObject() Methods" and "Other setXXX() Methods".

Note that there is nothing Oracle-specific about the functionality described here; it follows standard JDBC syntax.

The following example shows how to use a prepared statement to execute INSERT operations that add two rows to the EMP table. For the complete sample application, see "Inserting Names into the EMP Table--InsertExample.java".

    // Prepare to insert new names in the EMP table
    PreparedStatement pstmt = 
      conn.prepareStatement ("insert into EMP (EMPNO, ENAME) values (?, ?)");

    // Add LESLIE as employee number 1500
    pstmt.setInt (1, 1500);          // The first ? is for EMPNO
    pstmt.setString (2, "LESLIE");   // The second ? is for ENAME
    // Do the insertion
    pstmt.execute ();

    // Add MARSHA as employee number 507
    pstmt.setInt (1, 507);           // The first ? is for EMPNO
    pstmt.setString (2, "MARSHA");   // The second ? is for ENAME
    // Do the insertion
    pstmt.execute ();

    // Close the statement
    pstmt.close();

Commit Changes

By default, DML operations (INSERT, UPDATE, DELETE) are committed automatically as soon as they are executed. This is known as auto-commit mode. You can, however, disable auto-commit mode with the following method call on the Connection object:

conn.setAutoCommit(false);

(For further discussion of auto-commit mode and an example of disabling it, see "Disabling Auto-Commit Mode".)

If you disable auto-commit mode, then you must manually commit or roll back changes with the appropriate method call on the Connection object:

conn.commit();

or:

conn.rollback();

A COMMIT or ROLLBACK operation affects all DML statements executed since the last COMMIT or ROLLBACK.

Important: If auto-commit mode is disabled and you close the connection without explicitly committing or rolling back your last changes, then an implicit COMMIT operation is executed. Any DDL operation, such as CREATE or ALTER, always includes an implicit COMMIT. If auto-commit mode is disabled, this implicit COMMIT will not only commit the DDL statement, but also any pending DML operations that had not yet been explicitly committed or rolled back.

Close the Connection

You must close your connection to the database once you finish your work. Use the close() method of the Connection object to do this:

conn.close();

Note: Typically, you should put close() statements in a finally clause.

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